protected override Expression VisitProjection(ProjectionExpression proj)
{
if (isTopLevel)
{
isTopLevel = false;
this.currentSelect = proj.Select;
Expression projector = this.Visit(proj.Projector);
if (projector != proj.Projector || this.currentSelect != proj.Select)
{
return(new ProjectionExpression(this.currentSelect, projector, proj.Aggregator));
}
return(proj);
}
if (proj.IsSingleton && this.CanJoinOnServer(this.currentSelect))
{
TableAlias newAlias = new TableAlias();
this.currentSelect = this.currentSelect.AddRedundantSelect(this.language, newAlias);
// remap any references to the outer select to the new alias;
SelectExpression source = (SelectExpression)ColumnMapper.Map(proj.Select, newAlias, this.currentSelect.Alias);
// add outer-join test
ProjectionExpression pex = this.language.AddOuterJoinTest(new ProjectionExpression(source, proj.Projector));
var pc = ColumnProjector.ProjectColumns(this.language, pex.Projector, this.currentSelect.Columns, this.currentSelect.Alias, newAlias, proj.Select.Alias);
JoinExpression join = new JoinExpression(JoinType.OuterApply, this.currentSelect.From, pex.Select, null);
this.currentSelect = new SelectExpression(this.currentSelect.Alias, pc.Columns, join, null);
return(this.Visit(pc.Projector));
}
var saveTop = this.isTopLevel;
var saveSelect = this.currentSelect;
this.isTopLevel = true;
this.currentSelect = null;
Expression result = base.VisitProjection(proj);
this.isTopLevel = saveTop;
this.currentSelect = saveSelect;
return(result);
}
protected override Expression VisitProjection(ProjectionExpression proj)
{
SelectExpression save = this.currentSelect;
this.currentSelect = proj.Select;
try
{
if (!this.isTopLevel)
{
if (this.CanJoinOnClient(this.currentSelect))
{
// make a query that combines all the constraints from the outer queries into a single select
SelectExpression newOuterSelect = (SelectExpression)QueryDuplicator.Duplicate(save);
// remap any references to the outer select to the new alias;
SelectExpression newInnerSelect = (SelectExpression)ColumnMapper.Map(proj.Select, newOuterSelect.Alias, save.Alias);
// add outer-join test
ProjectionExpression newInnerProjection = this.language.AddOuterJoinTest(new ProjectionExpression(newInnerSelect, proj.Projector));
newInnerSelect = newInnerProjection.Select;
Expression newProjector = newInnerProjection.Projector;
TableAlias newAlias = new TableAlias();
var pc = ColumnProjector.ProjectColumns(this.language, newProjector, null, newAlias, newOuterSelect.Alias, newInnerSelect.Alias);
JoinExpression join = new JoinExpression(JoinType.OuterApply, newOuterSelect, newInnerSelect, null);
SelectExpression joinedSelect = new SelectExpression(newAlias, pc.Columns, join, null, null, null, proj.IsSingleton, null, null, false);
// apply client-join treatment recursively
this.currentSelect = joinedSelect;
newProjector = this.Visit(pc.Projector);
// compute keys (this only works if join condition was a single column comparison)
List <Expression> outerKeys = new List <Expression>();
List <Expression> innerKeys = new List <Expression>();
if (this.GetEquiJoinKeyExpressions(newInnerSelect.Where, newOuterSelect.Alias, outerKeys, innerKeys))
{
// outerKey needs to refer to the outer-scope's alias
var outerKey = outerKeys.Select(k => ColumnMapper.Map(k, save.Alias, newOuterSelect.Alias));
// innerKey needs to refer to the new alias for the select with the new join
var innerKey = innerKeys.Select(k => ColumnMapper.Map(k, joinedSelect.Alias, ((ColumnExpression)k).Alias));
ProjectionExpression newProjection = new ProjectionExpression(joinedSelect, newProjector, proj.Aggregator);
return(new ClientJoinExpression(newProjection, outerKey, innerKey));
}
}
else
{
bool saveJoin = this.canJoinOnClient;
this.canJoinOnClient = false;
var result = base.VisitProjection(proj);
this.canJoinOnClient = saveJoin;
return(result);
}
}
else
{
this.isTopLevel = false;
}
return(base.VisitProjection(proj));
}
finally
{
this.currentSelect = save;
}
}